1. Field
The invention relates to toolholders and more particularly those used for punching tools, and means for extending their useable life, with application to turret punches and punch blocks.
2. State of the Art
Repeated use of punch tools results in wear of the bores for guiding and positioning the toolholders, punching operations eventually becoming impractical because the toolholder is no longer sufficiently guided and centered with respect to the work piece. The wear on the bore is typically not uniform, so that replacement of the toolholder with one of larger diameter is not practical. Restoring the guiding bore to useable condition usually requires it be re-bored, which requires replacement of the toolholder with one of appropriately larger diameter. Thus, both the bore and the punch holder must be refurbished. The resulting toolholder is of non-standard size, leading to confusion in use. Re-boring of the toolholder bore generally requires complete dismantling of the turret punch press to send the turret to another facility for boring. It is very desirable that some method be available to refurbish the worn bore that permits the use of the original toolholder and avoids the lost time and cost of dismantling and re-boring. Equally desirable is a toolholder guide capable of long life while being easily repaired. One method for refurbishment is disclosed in U.S. Pat. No. 4,240,314. This method involves the drilling of spaced side bores into the toolholder wall and the insertion of plugs of resilient material into the bores to position the toolholder away from the wall. The plugs extend outwardly into the toolholder bore sufficiently so that the toolholder compresses the resilient plugs tightly into the side bores. The toolholder reciprocates across the ends of the plugs. The small plugs provide limited bearing surface and wear soon occurs requiring the replacement of the plugs, although their resilient springback extends the useful life somewhat. The plastic tends to creep under constantly applied load so that the advantage of the compression is largely lost. This method is therefore of severely limited value, either for repair or for original equipment.